Picture signal processing apparatuses are categorized as two types. The first type is an apparatus having a structure of which a picture signal is stored as time elapses. The second type is an apparatus using a class categorizing adaptive process proposed by the applicant of the present invention. Exemplifying a noise eliminating process, FIG. 1 shows the structure of which a picture signal is stored as time elapses. This structure is known as a motion adaptive type recursive filter.
An input picture signal is supplied to an adding circuit 2 through an amplifier 1 that adjusts the amplitude of the input picture signal in such a manner that one pixel is supplied at a time. An output picture signal of a frame that immediately precedes the current frame (namely, the current frame of an input picture signal (hereinafter referred to as current frame) has been stored in a frame memory 3. (The frame that immediately precedes the current frame is referred to as preceding frame.) The picture signal stored in the frame memory 3 is read successively pixel by pixel corresponding to pixel positions of the input picture signal and supplied to the adding circuit 2 through an amplifier 4 that adjusts the amplitude of the picture signal.
The adding circuit 2 adds a pixel of the current frame that is output from the amplifier 1 and a pixel of the preceding frame that is output from the amplifier 4 and outputs the added output as an output picture signal. In addition, the adding circuit 2 outputs the added output to the frame memory 3. The frame memory 3 rewrites the picture signal stored therein with the output picture signal of the adding circuit 2.
In addition, the input picture signal of the current frame is supplied pixel by pixel to a subtracting circuit 5. The picture signal of the preceding frame stored in the frame memory 3 is read pixel by pixel corresponding to the pixel positions of the input picture signal and supplied to the subtracting circuit 5. The subtracting circuit 5 outputs the difference between the pixel values of pixels at corresponding positions of pictures of the current frame and the preceding frame.
The difference that is output from the subtracting circuit 5 is supplied to an absolute value calculating circuit 6. The absolute value calculating circuit 6 calculates the absolute value of the difference that is output from the subtracting circuit 5. The calculated absolute value is supplied to a threshold value processing circuit 7. The threshold value processing circuit 7 compares the absolute value of the supplied difference of the pixel values with a predetermined threshold value and determines whether each pixel is a moving portion or a still portion. When the absolute value of the difference of the pixel values is smaller than the threshold value, the threshold value processing circuit 7 determines that the input pixel is a still portion. In contrast, when the absolute value of the difference of the pixel values is larger than the threshold value, the threshold value processing circuit 7 determines that the input pixel is a moving portion.
The determined result representing whether the input pixel is a still portion or a moving portion is supplied from the threshold value processing circuit 7 to a weighting coefficient generating circuit 8. The weighting coefficient generating circuit 8 designates a value of a weighting coefficient (0≦k≦1) corresponding to the determined result of the threshold value processing circuit 7 and supplies the designated coefficient k to the amplifier 1. In addition, the weighting coefficient generating circuit 8 supplies a coefficient (1−k) to the amplifier 4. The amplifier 1 multiplies the input signal by k. In contrast, the amplifier 4 multiplies the input signal by (1−k).
In this case, when the determined result of the threshold value processing circuit 7 represents that the pixel of the current frame is a still pixel, a constant value in the range of k=0 to 0.5 is designated as the value of the coefficient k. Thus, the output of the adding circuit 2 is a value of which the pixel values of the current frame and the preceding frame that have been weighted and added.
On the other hand, when the determined value of the threshold value processing circuit 7 represents that the pixel of the current frame is a moving portion, k=1 is designated as the value of the coefficient k. Thus, the adding circuit 2 outputs the pixel value of the current frame (namely, the pixel value of the input picture signal).
The stored signal of the frame memory 3 is rewritten frame by frame with the output picture signal of the adding circuit 2. Thus, a still portion of the picture signal stored in the frame memory 3 is a cumulated value of pixel values of a plurality of frames. Thus, assuming that noise varies in each frame at random, when weighted additions are performed, the noise gradually becomes small and is finally eliminated. Thus, noise is eliminated from a still portion of a picture signal stored in the frame memory 3 (the still portion is the same as an output picture signal).
However, when noise is eliminated using the motion adaptive type recursive filter, the following problems arise.
When a noise level is large, a moving portion may be mistakenly detected as a still portion. In this case, the picture quality may deteriorate (for example, the picture may become unsharp). In addition, noise cannot be eliminated from a moving portion.
On the other hand, a noise eliminating apparatus using the class categorizing adaptive process has been proposed by the applicant of the present invention. In the class categorizing adaptive process, noise can be eliminated regardless of whether a pixel of a still portion or a moving portion. However, the motion adaptive type recursive filter has a higher noise eliminating performance than the noise eliminating apparatus using the class categorizing adaptive process.
Besides the noise eliminating process, the present invention can be effectively applied for a resolution converting apparatus that increases the resolution of an input picture signal.
In other words, at present, there are a variety of television systems that are for example so-called standard systems of which the number of scanning lines per frame is 525 or 625 and high resolution systems of which the number of scanning lines per frame is larger than that of the standard systems (for example, high vision system using 1125 scanning lines).
In this case, to allow an apparatus corresponding to for example a high resolution system to handle a picture signal corresponding to the standard system, it is necessary to convert a picture signal with a resolution corresponding to the standard system into a picture signal with a resolution corresponding to the high resolution system (this process is sometimes referred to as upconvert). To solve such a problem, various types of resolution converting apparatuses using linear interpolating method and so forth have been proposed. For example, upconvert using storage type process and upconvert using class categorizing adaptive process have been proposed.
In a resolution converting apparatus using storage type process that outputs a converted output picture, although a still picture portion less deteriorates, a large moving portion deteriorates. On the other hand, in a resolution converting apparatus using class categorizing adaptive process that outputs a converted output picture, although a moving picture portion less deteriorates, a still picture portion deteriorates.
In other words, so far, it was difficult to accomplish a resolution converting apparatus that can form a picture that less deteriorates for both a still picture portion and a moving picture portion.
Thus, an object of the present invention is to provide a picture processing apparatus, a picture processing method, a program, and a record medium that allow an advantage of a structure of which a picture signal is stored as time elapses and an advantage of a structure of which a class categorizing adaptive process is used to be effectively used so as to perform a good process as a whole.